This invention relates to multi-layer articles in which one of the layers is a fluoroplastic.
Fluorine-containing polymers (also known as xe2x80x9cfluoropolymersxe2x80x9d) are a commercially useful class of materials. Fluoropolymers include, for example, crosslinked fluoroelastomers and semi-crystalline or glassy fluoroplastics. Fluoroplastics are generally of high thermal stability and are particularly useful at high temperatures. They may also exhibit extreme toughness and flexibility at very low temperatures. Many of these fluoroplastics are almost totally insoluble in a wide variety of solvents and are generally chemically resistant. Some have extremely low dielectric loss and high dielectric strength, and may have unique non-adhesive and low friction properties. See, e.g., F. W. Billmeyer, Textbook of Polymer Science, 3d ed., pp. 398-403, John Wiley and Sons, New York (1984).
Fluoroelastomers, particularly the copolymers of vinylidene fluoride with other ethylenically unsaturated halogenated monomers such as hexafluoropropylene, have particular utility in high temperature applications such as seals, gaskets, and linings. See, e.g., R. A. Brullo, xe2x80x9cFluoroelastomer Rubber for Automotive Applications,xe2x80x9d Automotive Elastomer and Design, June 1985; xe2x80x9cFluoroelastomer Seal Up Automotive Future,xe2x80x9d Materials Engineering, October 1988; and W. M. Grootaert et al., xe2x80x9cFluorocarbon Elastomers,xe2x80x9d Kirk-Othmer, Encyclopedia of Chemical Technology, vol. 8, pp. 990-1005 (4th ed., John Wiley and Sons, 1993).
In the automotive industry, increased concern with evaporative fuel standards has led to the need for fuel system components that have improved barrier properties. This helps reduce the permeation of fuel vapors through automotive elements such as fuel filler lines, fuel supply lines, fuel tanks, and other elements of an automobile fuel system. Multi-layer tubing and other articles containing a fluoropolymer layer have been used in such automotive elements to provide a chemically resistant permeation barrier. For example, multi-layer -articles in which a tetrafluoroethylene-vinylidene fluoride-hexafluoropropylene (TFE-VDF-HFP) fluoroplastic layer is bonded on one face to a relatively thin inner layer made of an elastomer (e.g., a fluoroelastomer or a non-fluorinated elastomer such as nitrile rubber or epichlorohydrin rubber) and on the other face to a relatively thick outer coverstock layer have been used for this purpose.
The invention relates to the discovery that multi-layer articles featuring a fluoroplastic layer bonded to a non-fluorinated polymer layer exhibit useful properties such as good fuel permeation resistance when the fluoroplastic has a melting point of at least 200xc2x0 C. and contains interpolymerized units of at least TFE and VDF, and the amount of VDF is at least 0.1% by weight, but less than than 20% by weight. Preferably, the amount of vinylidene fluoride units is at least 3% by weight, more preferably between 3 and 15% by weight, and even more preferably between 10 and 15% by weight. Also useful are fluoroplastics that include at least TFE and VDF units in which the amount of VDF units is between 0.1 and 15% by weight, more preferably between 3 and 15% by weight, and even more preferably between 10 and 15% by weight. Such fluoroplastics may optionally have melting points greater than 200xc2x0 C. The adhesion between the two layers preferably is at least 5 N/cm, more preferably at least 15 N/cm, measured in accordance with ASTM D 1876 (T-Peel test).
Other monomers that may be interpolymerized with the TFE and VDF monomers include hexafluoropropylene (HFP), olefin monomers, and perfluorinated alkyl or alkoxy vinyl ether monomers (e.g., in an amount ranging from 0.1 to 5% by weight). One useful fluoroplastic includes interpolymerized units derived from 0.1-15% (preferably 10-15%) by weight VDF, 60-85% by weight TFE, and 10-30% by weight HFP. The fluoroplastic may have a multi-modal molecular weight distribution to facilitate processing, or it may have a uni-modal molecular weight distribution.
The non-fluorinated polymer layer may be an elastomer or a thermoplastic polymer. Thermoplastic elastomers may also be used. The multi-layer article may further include a third polymer layer bonded to the first polymer layer such that the first polymer layer is interposed between the second and third polymer layers. Suitable materials for the third polymer layer include elastomers. The elastomers may be fluorinated or non-fluorinated.
Any or all of the layers of the multi-layer article may be electrically conductive. Preferably, however, it is the innermost layer that is electrically conductive, where xe2x80x9cinnermostxe2x80x9d refers to the layer designed to contact, e.g., fuel or other liquid. Thus, for example, in a two-layer construction, it is the fluoroplastic layer that typically is electrically conductive, while in a three-layer construction, where the fluoroplastic layer is interposed between the second and third polymer layers described above, it is the third polymer layer that typically is electrically conductive.
The individual layers of the article may be bonded directly to each other. Alternatively, they may be bonded together by means of a bonding layer such as a polyamine. A particularly useful polyamine for this purpose is polyallylamine having a molecular weight of greater than 1,000.
The multi-layer articles may be provided in a wide variety of shapes, including sheets, films, containers, hoses, tubes, and the like. The articles are especially useful wherever chemical resistance and/or barrier properties are necessary. Examples of specific uses for the articles include their use in rigid and flexible retroreflective sheets, adhesive articles such as adhesive tapes, paint replacement films, drag reduction films, fuel line and filler neck hoses, hydraulic fluid hoses, exhaust handling hoses, fuel tanks, and the like. The articles are also useful in chemical handling and processing applications, and as wire and cable coatings or jackets.